Telegraph system



Oct. 28, 1930. A. A. CLOKEY TELEGRAPH SYSTEM Filed Dec. 26, 1928 INVENTOR ALLISON A .CLOKEY aw? V ATTORNEY Patented Oct. 28, 193% ES FATE Wait orisi ALLISON ANDREW CLOKEY, 0F RUTHERFORD, NEW d'mSE-Y, ASSIGNOR TO ENTER- NATIONAL STANDARD ELECTRIC CORPORATION, 9F NEW YORK, 33'. Y.

TELEGRAPH SYSTEM Application filed December 26, 1928, Serial No.

This invention relates to synchronous telegraph systems and particularly to such systems for use on cables of high capacity.

An object of the invention is to maintain synchronism between transmitting and receiving terminal equipment, and to eliminate false corrections of the receiving apparatus due to phase shift of the signals during transmission.

Synchronous telegraph systems heretofore employed have utilized'synchronizing impulses derived from the received signal impulses themselves "for synchronizing the receiving apparatus. This method has the advantages that the entire line time may he used for signal transmission and that synchronizing impulses occur at very frequent intervals.

However, there is an objection to synchronizing from signal impulses. it is that, even though the receiving apparatus be running in perfect phase adjustment with the transmitting apparatus, received signal impulses may, due to line distortion, arrive at the receiving station out of phase with the receiving apparatus and cause false corrections which alternately advance and retard the phase of the receiving apparatus. a

The phase shift in the received signals is caused primarily by the non-uniform nature of the signal impulses. For instance, a preponderance of positive impulses during a given time interval may shift the phase of the received impulses in one direction and a preponderance of negative impulses may shift the phase in the opposite direction.

To eliminate false corrections it is proposed, in accordance with this'invention, to eliminate the use of signal impulses for correction purposes and to transmit at intervals, in place of signals, a series of clearing out impulses comprising a ground impulse, or a series of equal impulses of alternately opposite polarity, or both, and thereafter aspecial synchronizing impulse. The grounding nnpulse and/or the series of pulses of alternately opposite polarity leave the cable in a new tral condition regardless of the ,character of the preceding signal impulses, so that successive synchronizing impulses, as received, al-

328518, and in Great Britain Geto'ber 17, 1928.

ways hear the same phase relation to the transmitting apparatus. The time required to neutralize the cable preparatory to the transmission of the synchronizing impulses is not available for signal transmission hut the is a diagram representing schematically the apparatus at a transmitting station and Fig. 3, a diagram representing the apparatus at a receiving station. Fig. 4 shows the curve representing the phase of the received current relative to the segments of the receiving distributor.

Theory 0 f the invemion An understanding of the manner in which this invention eliminates false corrections of synchronous receiving apparatus for cable signals may he readily conveyed with the aid of curves of signals as they are transmitted and received. in Fig. l, the upper curve 75 represents a series of signal impulses as they are transmitted and curve 76 represents the same signals as they may appear after having been transmitted over a submarine cahle, shaped, and amplified for the operation of signal recording and synchronizing equipment.

lit will he noted that whereas the transmitted impulses are square topped, the received current rises gradually and requires appreciable time, following each reversal, to rise to a value sufficient to operate a receiving relay or a phase correcting relay. in connection with curve 76, the lines '57 and 79, above and below the zero axis 78, indicate the current values necessary to operate a phase correcting relay. Thus a positive impulse applied to the cable at time A does not increase the potential of the receiving end of the cable suficient to operate a correcting relay until time A, .18 seconds later. Such time lag between transmission and reception is unavoidable and would have no bad effeet were it uniform, but unfortunately it varies between wide limits depending on the sequence of signals transmitted. In the case illustrated it may vary from .12 seconds,

I at time J, to .18 seconds, at time A, depending on the sequence of preceding impulses.

In a system in which any or all of the received signal impulses are used for correction purposes, this non-uniform spacing of received impulses may cause needless false corrections because at time A, a signal is received later, with respect to the distant transmitting distributor, than is the signal at time K, although there has been no actual phase shift between the transmitting and receiving equipment.

But although, as indicated, there is a variation in the transmission time when heterogeneous impulses are sent, it will be seen that on sending pure reversals (from time F on) the transmission interval becomes constant after a few reversals. In accordance with this invention, synchronous corrections are made only following a train of reversals, or a grounding period, or some other treatment. The only requirement is thatthe treatment of the cable preceding correction be such as to restore it each time to a definite predetermined condition.

In the case illustrated the treatment is a series of reversals because that hasbeen found satisfactory with some cables, but other methods may be more satisfactory under other conditions. Furthermore, with the method illustrated, the number of reversals necessary will vary with the length and type of cable and with the shaping networks used at the terminals. The treatment necessary to secure a uniform transmission interval may be determined for any application by methods well known in the art, such as by measurement of oscillographic records of received signals.

Description of apparatus Referring to Fig. 2, a submarine cable 1, arranged for duplex operation, is connected by a conductor 2 to the common ring 3 of a transmitting distributor. For the purpose of explanation the distributor rings have been shown developed, but it is to be understood that in practice they Would be in .the form of a disc or cylindrical surface and that the brushes 4 and 5 would be revolved by a eon stant speed motor 7, which has been shown as a phonic wheel excited from a source of constant frequency current 0.

Each of the segments successively associated bybrush 4 with the common transmitting ring 3 is normally connected, either directly or through contacts associated with the relays 9 and 10, with one of the transmitting tongues of a tape transmitter. The system, as shown,

is arranged for four channel operation and comprises four tape transmitters, A B C and D. When no signals are being transmitted, .all the tongues of the transmitting tongues lie against their left contacts, which in the case of channels A and C are connected to a currentsouree of negative polarity, and in the case of channels B and D are connected to sources of current of positive polarity. When signals are being transmitted, the transmitting tongues are moved in response to the perforations in the transmitting tapes to transmit positive or negative impulses in accordance therewith.

To the right of the synchronous motor 7 is shown an automatic switch which is operated from the shaft of motor 7 and which closes, at definitely measured, long intervals, a circuit comprising relays 9 and 10 to cause the transmission of signal impulses to be interrupted for one complete revolution of the brushes 4 and 5 while the cable is stabilized, and synchronizing impulses are transmitted. Cam 21 closes contact 28 at relatively long intervals, while cam 22 geared directly to motor shaft closes contact 27 with greater precision relatively to position of brushes. A detailed description of the operation of relays 9 and 10 and the circuits controlled thereby will be given later.

In Fig. 3, the receiving common ring 12 of a receiving distributor and the associated printer apparatus in channels A B C and D is connected to the cable 1, across the arms of the duplex bridge comprising condenser 13 and 1 1. The receiving brushes 15 and 16, like those at the transmitting station, are revolved overtheir associated common and segmented rings by a constant speed motor 17 controlled by a tuning fork 18. The frequency of fork 18, and hence the speed of motor 17, may be regulated by shifting weight 19 along the tines of the fork. A mechanism 20 is shown for automatically regulating fork 18 under control of received synchronizing impulses. To the right of motor 17 is an automatic timing switch similar to that shown at the transmitting station in Fig. 1, and designed to close its contacts simultaneously with the mechanism at the transmitting station.

Operation. of fransnaifting apparatus Normally the brushes 4 and 5 at the transmitting station in Fig. 2 successively connect the tongues of the transmitters in the dillerent channels A B C and D to the cable 1. and transmit impulses in accordance with the perforations in the transmitting tapes. This condition prevails for a predetermined period, which may vary from a few seconds to several minutes depending on the constancy of speed of the driving motors, at the end of which time, the cams 21 and 22 close their associated contacts, 28 and 27 simultaneously. lhe ratios of the speeds of cams 2i and 22 to each other and to the distributor shaft are so regulated that they close the contacts during an interval when the brushes 4 and 5 are travelling between segments 24 and 25, and remain closed during approximately one revolution and a half of brushes i and 5, i. e. until brushes 4 and 5 are travelling between segments 25 and 23 over channels C and l).

Following a closure of contacts 27 and 28, brush 5 applies ground from common ring 6 to segment 26, which closes a circuit through the winding of relay 9. conductor 29, resistance and contacts 28, and 27 to battery 81. Currentirom battery 81 thereupon operates relay 9, which locks up over its front contact and remains operated until brush 5 has completed a revolution, and contacts with release segment 25. lln the meantime .brush 5 contacts with segment 24 and operates relay 16 by closing a path from ground over common ring 6, through brush 5, segment 24, the winding of relay l0, conductor 32, resistance 33 and contacts 28 and 27 to the grounded battery 31. Relay l0 thereupon operates and locks up over its two independent tongues and front contacts against the opening of contacts 27 and 28. llt is released by brush 5 applying ground to segment 23.

While brush 5 is travelling from segment 23 to segment 25, brush l crosses the transmitting segments associated with channels A and B. No signals are being transmitted from these channels at this time because the tape transmitters have been locked by their locking magnets 34 and 35, which were energized over the two lower tongues and contacts of relay 9 whenthe latter operated. Since, when they are locked, the transmitting tongues of channel A lie against their negative contacts and the tongues of transmitter B lie against their positive contacts, channel A would transmit a series oil 5 negative impulses and channel B a series of posi tive impulses. By the operation of relay 9, however, the first and second segments of channel A were disconnected from their associated transmitting tongues and connected to ground over the contacts 38 and 39, while the fourth segments was connected to positive battery over contact 40. At the same time, the second, third and fourth segments of channel B were disconnected from their associated transmitting tongues, the second and third segments being connected to ground at contacts 41, and the fourth segment being connected to negative battery at contacts ll. Before brush 4 reaches the segments of the 3rd and 4th channels the 2nd and 3rd and 4th segments of channels 0 and the 2nd and 3rd segments of channels D have also been switched, by relay 10, from their associated transmitting tongues, to connection with positive or negative battery as required to tlow of current from battery 31 through the winding of relay 9, and causes the relay to release. This releases the tape transmitter magnets 34: and 35 in channels A and B and reconnects the transmitter tongues with their associated segments, so that when brush 4:

begins its next revolution, signals will be transmitted from channels A and B. Relay 9 may re-energize on brush 5 again applying ground to segment 26 but the ofl'ering of contacts 27 and 28 before brushes 4 and 5 reach channels A and B will restore the signalling conditions. Brush 5 applies ground from common ring 6 over segment 23 to'conductor 32, shunting the winding of relay l0 and causing the latter to release and as the contacts 27 and 28 are by this timeopen relay 10 does not energize again when brush "5 passes over contact 24. The release of relay l0 releases the transmitter locking magnets 36 and37 in channels G and 1D and connects the trans mitting tongues of those channels to their associated transmitting segmentsso that signal transmission will be also resumed from channels C and D. I 7

Operation of receieing apparatus Referring to Fig. 3, at the receiving station, cams 70 and 71 close their associated contacts 72 and 73 simultaneously with the contacts 27 and-28 at the transmitting station. Hence, when brush 16 contacts with segment 45, it closes a circuit from ground over coon ring 46, segment 45, winding of relay 53, conductor 5%, resistance 57, and con tacts 72 and 73 to battery 58, whereupon relay 53 operates and locks up overits ,upper armature and grounded contact. lit completes, at the same time, over its lower contacts, circuits including the windings of locking magnets 48 and 49 in channels A and B, which are thereupon energized.

The brushes continue their travel, and after a halt revolution, close a circuit from ground over'common ring 46, segment 43,

the winding of relay 52, conductor 55, resistance 56 and contacts 7 2 and 73 to battery 58, which operates relay 52, the latter looking up over its upper armature and grounded contact, and also a lower tongue and contact against opening of contacts 72 and 73.

By the operation of relay 52 the two inside 50 and 51 at the receiving station areenergized to prevent the receiving apparatus from responding to the series of pulses of alternately opposite polarity which are transmitted for line clearing purposes.

Synchronizing the receiving apparatus While the brushes at the transmitting end receiving stations are travelling over the segments associated with channels A B and C, any distorting influence on the cable due to the history of previous signal impulses is being wiped out, and it is undesirable during this period that any correction be attempted at the receiving station. By the time the brushes have reached channel D, however, the cable has been stabilized and received current reversals may be utilized for correction purposes without danger of making false corrections. Special synchronizing segments 59 and 60 are therefore inserted between the second and third, and between the fourth and fifth receiving segments of channel D. There is no practical difficulty in inserting these extra segments at these points because it is customary to make the receiving segments only a half or a third as long as the transmitting segments. Segments 59 and 60 being spaced equidistant between receiving segments, are in positions to receive reversals, that is assuming there is no deviation from synchronism between the transmitting and receiving apparatus, brush 15 will connect segments 59 and 60 to the common ring 47 just asreceived current im-- pulses are passing through zero, while changing from positive to negative. This condition is shown to better advantage in Fig. 4. It will be seen by referring to Fig. 4, that if the receiving distributor is slightly out of phase with the transmitting distributor, the Wave 76 will be shifted forward or backward relative to segments 59 and 60 and either positive or negative impulses will be applied to segments 59 and 60. Since these segments are connected, through contacts 61 on relay 52, to the Winding of polar relay 62, the latter relay will move its tongue to the left or to the right in response thereto. If the receiving dist-ributor'is running in advance of the received signals negative impulses will be applied over the segments 59 and 60 to polar relay 62, which will cause the tongue of that relay to move momentarily to the right and close a circuit from battery 63 through the relay tongue and right contact to correcting magnet 64, which steps the ratchet wheel 66 to the right and moves the weight 19 on the tuning fork 18 toward the end of the tines and reduces the speed of the fork. On the other hand, if the receiving apparatus is running slower than the sending apparatus,

positive impulses will be applied to segments 59 and 60 and hence to relay 62, moving the tongue of the latter relay to the left. This applies current from battery 63 over the tongue and left contact of relay 62 to corrector magnet 65, which steps the ratchet Wheel 67 to the left and moves weight 19 toward the base of the fork thus increasing its frequency and speeding up the receiving apparatus.

Although a simple tuning fork 18 has been shown as a source of oscillations for the constant speed motor 17, it is to be understood that the invention is not limited to the use of. such apparatus. In fact, since for the highest efiiciency it is desirable with this system to correct only at long intervals, extremely constant speed drives should be utilized. Vacuum tube regenerative tuning forks have been developed to a high degree of perfection and are desirable for use in this system. Furthermore, although means has been shown for correcting the speed of the receiving distributor in either direction,

it is Within the scope of this invention to cause the receiving distributor to run either slightly faster or slightly slower than the transmitting distributor and to correct the receiving distributor periodically on one direction only. Systems employing both primary and secondary correction may also be used. Such a system is disclosed in United States Patent to Pernot No. 1,647,468, patented November 1, 1927, in which the distributor arms carrying the brushes are stepped backward or forward (clock hand correction) to take care immediately of any departure of the distributor brushes from the desired phase position, while the natural period of the controlling tuning fork is changed to prevent, as much as possible, the necessity of future clock hand corrections.

Furthermore I do not limit the application of my invention to synchronous systems em ploying rotary current distributors using the Bandst code, nor to the suspension of signals for one revolution of the distributor, nor to the transmission of grounding impulses and current reversals in the particular order disclosed. Theinvention is applicable to synchronous systems of various types, including those in which contacts are periodically closed by rotating cams or vibrating reeds. The length of the period during which signal transmission is suspended for stabilizing purposes is determined by the characteristics of the cable to which it is applied, and may be less or greater thanthe time of a complete cycle of operation of the synchronous apparatus. Likewise the character of the arraeea treatment may be to ground, or open, the

cable for the entire period preceding the synchronizing impulse. Under some conditions one synchronizing impulse may be suficient for synchronizing purposes and under others a series of several impulses may be required.

lln view of the above facts it is clear that the invention is not limited to the particular disclosure in the drawings but only as delined in the following claims.

Claims.

lxThe method of signalling over a high capacity cable which comprises transmitting signal impulses, interrupting the signal transmission at intervals and before resuming signal transmission, restoring the cable to v a predetermined electrical condition and thereafter transmitting a synchronizing impulse.

2. The method of signalling over a high capacity cable which comprises signalling for an interval, thereafter clearing the cable of unbalanced residual charges and thereafter transmitting a synchronizing impulse.

3. The method of signalling over a high. capacitycable which comprises signalling for periodic intervals and during intervening periods transmitting a series of clearing out pulses of alternately opposite polarity.

4. The method of signalling over a high capacity cable which comprises transmitting and receiving signal impulses for an interval of time, thereafter transmitting for a shorter interval of time a series of equal clearing out impulses of alternately opposite polarity, and thereafter transmitting and re ceiving a synchronizing impulse.

5. The method of signalling over a high capacity cable which comprises transmitting a series of si al impulses, thereafter grounding the cable at the transmitting station, and thereafter transmitting a synchronizing impulse.

\ 6. The method of signalling over a high capacity cable which comprises transmitting signal impulses for a predetermined period, thereafter grounding the cable for a predetermined interval, thereafter transmitting equal impulses, of L alternately opposite polarity for a predetermined interval,- and thereafter transmitting synchronizing impulses. 1

' 7. The method of signalling over ahigh capacity cable which comprises transmitting signalling impulses for a predetermined interval of time, thereafter transmitting equal impulses of alternately opposite polarity for a predetermined interval, thereafter grounding the cable for a predetermined interval, and thereafter transmitting a synchrenizing impulse.

8. in a synchronous telegraph system comprising a high capacity cable, transmitting means for transmitting thereto, in succession, a series of signal impulses, a series of equal clearingout impulses of alternately opposite polarity and a synchronizing impulse.

9. in a synchronous telegraph system comprising a high capacity cable, transmitting means for transmitting thereto in succession, a series of signal impulses, a grounding impulse, a series of equal impulses of alternately opposite polarity, and synchronizing impulse.

10. In a synchronous telegraph system comprising a high capacity cable, transmitting means for transmitting thereto in succession a series of signal impulses, a grounding impulse, a series of signal impulses ofalternately opposite polarity, and a synchronizing impulse; and receiving means operating synchronously with said transmitting means. comprising means ior receiving and recording (or repeating) signals, synchronizing means responsive to said synchronizing impulse for synchronizing said receiving means, and timing means for rendering said signal receiving means responsive to impulses received over the cable only when signal impulses are being transmitted and for rendering said synchronizing means responsive to impulses received over the cable only when synchronizing impulses are being received. L

' 11. In a synchronizing telegraph system comprising a high capacity cable, means at one end of said cable tortransmitting signal impulses thereto, means for grounding said conductor of said cable, means for transmitting equal impulses of alternately opposite polarity, and timing means for causing said first means to transmit signals to said conductor for a predetermined interval, for causing said second 'means to ground said conductor for a predetermined period thereafter, and for causing said third means to transmit to said conductor equal impulses of alternately opposite polarity for a predetermined interval thereafter, and means at the opposite end of said cable operating synchronously with the transmitting means for receiving said signal impulses and said synchronizing impulse. I p

ALLISON ANDREW CLOKEY. 

